A significant amount of the development efforts in the container industry continues to be directed toward reducing material requirements and thus material costs in order to gain a competitive advantage. For instance, in the case of drawn and ironed ("D/I") containers the geometry/configuration of various portions of the container body have been modified in order to maintain/increase the strength of the container body to accommodate a reduction in the gauge of sheet metal from which the bodies are formed. Moreover, material requirements have been reduced for D/I containers by necking the open end of the container body to reduce its diameter and thus the diameter of the end piece required to seal the container body.
In order to further realize the benefits associated with necking, multiple necking operations have been implemented to reduce the diameter of the end piece to an even greater extent. However, performing multiple necking operations, particularly when using thinner gauges of sheet metal, may increase the potential for wrinkling and/or other types of metal deformation of the container body. Moreover, alignment problems in multiple necking operations may cause damage to the container body due, for instance, to an undesired impact between the container body and a necking die. In addition, misalignment of the container body with a necking die may also produce a necked portion which is not concentric with the container's sidewall. This may cause problems in subsequent container body processing, such as when seaming the end piece onto the necked portion and which may result in a defective seal. These types of defects often require that the container body be scrapped, thereby increasing material requirements.
In addition to the reduction of material requirements, significant development efforts have also been directed toward increasing the production rate of the overall container body forming process. Specifically with regard to die necking operations, production rates may be increased by increasing the speed at which the container body is axially advanced relative to the necking die. However, this increase in speed may cause a number of problems, particularly in multiple necking operations. For instance, after an initial necking operation portions of the container body are typically unsupported in one or more subsequent necking operations such that the potential for wrinkling and/or other metal deformation of these portions exists, due for instance to the increase in hydraulic-type pressures being exerted on such unsupported portions at the desired increased speeds. Moreover, the effects of any misalignment of the container body with the necking die may be magnified at increased production speeds. Consequently, increases in production speed may be accompanied by an increase in the number of container bodies which are scrapped.
Based upon the foregoing, it can be appreciated that it would be desirable to take advantage of the reduction in material requirements associated with multiple necking operations, particularly at increased production speeds, while reducing the number of defects introduced into container bodies when undergoing multiple necking operations and thus reducing material requirements.